1. Field of the Invention
The present invention relates to a method for fabricating a microactuator for an inkjet head, and more particularly to a method for fabricating such a microactuator, which achieves an easy formation of oxide piezoelectric elements having a desired pattern, using a patterning process mainly used in the fabrication of semiconductor devices.
2. Description of the Prior Art
Generally, microactuators, which are used for inkjet heads, include an actuating means for squirting or firing ink. For such an actuating means, heaters and piezoelectric elements are mainly used.
In the case of microactuators using piezoelectric elements, a PZT, which is an oxide piezoelectric material exhibiting a strong piezoelectric property, is mainly used for those piezoelectric elements.
Referring to FIG. 16, a conventional microactuator using such a PZT is illustrated. As shown in FIG. 16, the microactuator includes a PZT element 30 attached with lower and upper electrodes 20 and 40 at lower and upper surfaces thereof, respectively. A vibrating plate 10 is attached to a surface of the lower electrode 20 opposite to the PZT element 30. The vibrating plate 10 is operatively coupled to the PZT element 30 so that it generates a mechanical deformation.
A chamber plate 50, which has a plurality of solution chambers 51, is attached to the vibrating plate 10 opposite to the PZT element 30. As the vibrating plate 10 is bent, ink is introduced into the solution chambers 51. Subsequently, the ink is outwardly squirted from the solution chambers 51 via nozzles (not shown).
The microactuator, which has the above mentioned structure including the PZT element 30, the lower and upper electrodes 20 and 40, and the vibrating plate 10, is typically fabricated using the following screen printing process or other simple bonding process.
In accordance with the screen printing process, a thin green sheet made of an oxide piezoelectric material, for example, a zirconium oxide (ZrO.sub.2), is first prepared. The green sheet is baked at a high temperature of at least about 1,000.degree. C., thereby forming a ceramic thin plate from which a vibrating plate 10 is, in turn, prepared. After the preparation of the vibrating plate 10, a conductive material such as platinum (Pt) is deposited to a thickness of 20 .mu.m or less on a desired portion of the vibrating plate 10, thereby forming a lower electrode 20.
PZT is then coated in a paste state over the upper surface of the lower electrode 20. An accurate lamination of the coated PZT is then conducted using a screen printing process, thereby forming a PZT layer having a very small thickness. The PZT layer is subsequently baked at a high temperature of about 1,000.degree. C. or less, thereby forming a PZT element 30.
Thereafter, gold (Au) is coated over the upper surface of the PZT element 30, thereby forming an upper electrode 40. Thus, a microactuator is produced.
In the case of such a microactuator having the above mentioned structure, the PZT element 30 expands and contracts longitudinally as high voltage is intermittently applied between the lower and upper electrodes 20 and 40, thereby causing the vibrating plate 10 to generate a mechanical deformation thereof. By such a mechanical deformation of the vibrating plate 10, a variation in volume occurs in the solution chamber 51 of the chamber plate 50 attached to the vibrating plate 10. As a result, ink is introduced into and outwardly squirted from the solution chambers 51.
The vibrating plate 10 may also be comprised of a stainless steel thin plate, in place of the ceramic thin plate. Where the vibrating plate 10 is comprised of such a metal thin plate, PZT elements are separately fabricated. In this case, a PZT sheet is bonded to the vibrating plate by means of an adhesive. The bonded PZT sheet is mechanically processed to form PZT elements of a desired pattern. Otherwise, a PZT sheet prepared to have a desired size is bonded to a stainless steel thin plate by means of an adhesive while being patterned on the stainless steel thin plate, thereby forming PZT elements of a desired pattern.
In the case of fabricating a microactuator using a ceramic thin plate as its vibrating plate, however, it is very difficult to form a vibrating plate having a desired thickness and an accurate size, using a zirconium oxide paste. Furthermore, there are difficulties due to a very high baking temperature used.
It is also difficult to form PZT elements of an accurate pattern by laminating and patterning a PZT paste on the vibrating plate in accordance with the screen printing process. In particular, the patterning process is conducted with a greatly degraded accuracy. Furthermore, a high baking temperature is required for the PZT paste, even though it is lower than that for the vibrating plate. Since such a PZT paste is typically baked at a temperature of about 900.degree. C. or less, there is a great degradation in the piezoelectric performance of the resulting PZT elements.
In the case of fabricating a microactuator using a metal thin plate, for example, a stainless steel thin plate, as its vibrating plate, the mechanical patterning process conducted to pattern a PZT sheet bonded to the stainless steel thin plate exhibits a very low accuracy. For this reason, there is dissatisfaction in terms of reliability and economical purposes. Where a PZT sheet prepared to have a desired size is bonded to the metal thin plate, a reduction in the yield of the resulting microactuator occurs. As a result, there is a degradation in the operating efficiency of the microactuator.